Officers were on patrol in Soham at about 11pm on Wednesday when they noticed the smell of the drug while in Fordham Road. They followed the scent to an industrial unit in Regal Drive.

Police forced their way into the premises and discovered the plants. Two people were living at the property and as police went in, one was able to escape, by jumping out of a window. The other was detained at the scene.

If police predictions about the value of the plants are correct, it will be the largest cannabis factory ever discovered in Cambridgeshire – with a haul more than three times the size of the previous biggest.

That was a factory at Tree Farm, in Haddenham, Cambs, which was raided in 2010, and led to the discovery of £1.75m worth of plants.

It comes at a time of seemingly increased activity by cannabis growers in the region.

In Norfolk, the offence has more than doubled in the last five years, with experts saying that a prolonged crackdown by police in London has forced growers and dealers to shift their operations out of the capital and into the regions – with East Anglia increasingly on the radar.

Following the latest discovery, a police spokesman said: “There were two people living at the factory in squalid conditions.

“When we tried to break the door down one of them jumped from a first-floor window (to evade arrest).

“We caught one of them with the help of a dog unit, but the other person remains at large.”

The man, who police believe is from Vietnam, was arrested on suspicion of producing cannabis and is in custody at Parkside Police Station, in Cambridge.

Inside the factory, police found plants at various stages of production and a compost heap from cultivated plants. Dozens of bags of fertiliser were also discovered.

The police spokesman estimated that the factory has been running for a year and the potential street value of the plants discovered is up to £6m.

Scenes of crime officers carried out investigations at the site yesterday to establish how many plants are in the unit. They are due to return today.

Sgt Dan Bramley, from Cambridgeshire Police, said: “This was good proactive work by the officers who tracked down the cannabis factory after noticing the smell.”